The five-time grand slam champion, a tournament wildcard, overcame Belarusian teenager Sabalenka 7-5, 7-6 (8) in a straight-sets victory on Sunday.
Sharapova, who made her comeback in April, is celebrating her first title since she won the Italian Open back in May 2015.
Sharapova trailed world No. 102 Sabalenka 4-1 and 5-1 in the first and second sets. But the 30-year-old Russian, who did not drop a set en route to Sunday's final, fought back on each occasion to claim her first title in 29 months.
Sharapova served a 15-month ban after she tested positive for the banned substance meldonium.
The former world number one was denied a wild card for the French Open, before missing Wimbledon through injury.
She was granted a wild card for the US Open and reached the fourth round before losing to Latvia's Anastasija Sevastova.